Sensors are used to monitor and measure a variety of biological conditions, such respiration, blood flow, and the like. As an example, an existing type of sensor may monitor a graft by placing the sensor at the graft in contact with the bloodstream. However, because use of such existing sensors contact with the bloodstream, such sensors may stimulate hypercellular processes to accelerate graft failure and/or or alter the graft mechanical structure. Accordingly, improved sensor designs are needed.